To restrict the cHanging Of Wallpaper

To disable changing of wallpaper

The Windows Picture and Fax Viewer will still allow people to select the Set as Desktop Background option upon right-clicking an image shown in the aforementioned system program.
You would be better advised to create an OU to host each of the machines on which you wish to restrict this option and adding an entry for a file called "Internet Explorer Wallpaper.bmp" in to the following Policy location:

Computer Configuration | Windows Settings | Security Settings | File System
If you add a file, simply select the location from your own machine and Windows will enter the file as %APPDATA%\Microsoft\Internet Explorer\Internet Explorer Wallpaper.bmp
If the file does not exist on your computer, navigate to a website, right-click an image (any image) and select Set as Background. This will create the file mentioned above and allow you select it from within Group Policy Editor.
You can also edit the registry (carefully, of course).
In the editor (Start > Run > regedit) navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\ActiveDesktop (It may be necessary to create the location).
Here, edit/create the DWORD value "NoChangingWallpaper" so that it's value is 1.